High voltage cascaded semiconductor amplifier including feedback and protective means



3,259,848 L11-1ER July 5, 1966 J. A. RADo HIGH VOLTAGE CASCADEDSEMICONDUCTOR AMP INCLUDING FEEDBACK AND PROTECTIVE MEANS 5 Sheets-Sheet1 Filed Nov. JB, 1963 July 5, 1966 J. A. RADo 3,259,848

HIGH VOLTAGE CASCADED SEMICONDUCTOR AMPLIFIER INCLUDING FEEDBACK ANDPROTECTIVE MEANS July 5, 1966 J. A. RADo 3,259,848

HIGH VOLTAGE CASCADED SEMIGONDUCTOR AMPLIFIER INCLUDING FEEDBACK ANDPROTECTIVE MEANS 3 Sheets-Sheet 5 Filed NOV. 18, 1963 ww M5@ .uw

\QN .NSM ww. @NNN United States Patent O 3,259,848 HIGH `VOLTAGECASCADED SEMICONDUCTOR AMPLIFIER INCLUDING FEEDBACK AND PRO- TEC'IIVEMEANS John A. Rade, Los Angeles, Calif., assigner to Hughes AircraftCompany, Culver City, Calif., a corporation of Delaware Filed Nov. 18,1963, Ser. No. 324,373 2 Claims. (Cl. 330-14) This invention relates tosemiconductor amplifiers and more particularly to such amplifiers forproviding output voltages larger than those which can be provided by asingle semiconductor.

Heretofore vacuum tube amplifiers have been used to supply largevoltages such as those used for electrostatic deflection of electronbeams in cathode ray tubes, but such amplifiers have the disadvantagesof large weight, volume, and power consumption. Attempts to overcomethese disadvantages by the use of semiconductors have had limitedsuccess because of the limited collector-toemitter breakdown potentialof individual semiconductors. Voltage dividing arrangements to overcomethis disadvantage by using semiconductors with their collectoremittercurrent paths in series have heretofore proved unreliable because ofdifiiculty in maintaining an unvarying division ratio among thesemiconductors over the signal cycle thereby resulting in subjectingindividual semiconductors to potential drops in excess of theirbreakdown ratings. Achieving linearity has also been a problem.

It is therefore an object of this invention to provide an improvedsemiconductor amplifier.

It is a further object of this invention to provide an improvedsemiconductor amplifier for supplying voltages larger than those whichcan be supplied by a single semiconductor.

Another object of this invention is to provide an improved semiconductoramplifier for supplying linear voltages larger than those which can besupplied by a single semiconductor.

It is a further object of this invention to provide an improvedamplifier for supplying voltages for electrostatic defiection ofelectron beams.

Briefly, in accordance with this invention a semi-conductor amplifier isprovided for supplying voltages larger than those which can be suppliedby a single semiconductor comprising a plurality of semiconductordevices each having a collector-emitter current path and a controlelectrode, the collector-emitter paths being connected in series betweena load impedance element connected to one source of operating potentialand a currentdetermining impedance element connected to another sourceof operating potential, and the control electrode of one of thesemiconductors being coupled to a source of input signals. The amplifieralso comprises biasing means including a stabilized voltage source foreach of the semiconductor devices other than the one whose controlelectrode is connected to the input signal source and a biascurrent-determining impedance element connected between each of thestabilized voltage sources and the control electrode of thecorresponding semiconductor device. Equal division of the output voltageamong the semiconductor devices in the series arrangement is obtained bymatching the semiconductor devices with respect to current gain andsuitably proportioning each base biasing impedance element. Diodeclamping between collector electrodes and stabilized voltage sourcesprotects each semiconductor device requiring such special protectionfrom exceeding its rated collector-to-emitter breakdown voltage duringits nonconducting phases. Linearity is improved by two inverse feedbackloops, one within 3,259,848 Patented July 5, 1966 ice a preamplifiercomprising part of the input signal source and the other between thefinal output of the series arrangement of semiconductor devices and theinput of the preamplifier.

The novel features of this invention, both as to its organization andmethod of operation will best be understood from the accompanyingdescription of a specific exemplary embodiment taken in connection withthe accompanying drawings, in which like characters refer to like parts,and in which:

FIG. l is a block diagram of a semiconductor amplifier provided linaccordance with this invention for providing voltages for electrostaticdefiection of an electron beam in a cathode ray tube;

FIG. 2 is a schematic circuit diagram of the semiconductor amplifier ofFIG. 1;

FIG. 3 is a diagram of voltage waveforms for explaining the operation ofthe circuit of FIG. 2; and

FIGS. 4a, 4b and 4c are simplified diagrams of a portion of a cathoderay tube to help in describing the final output of the circuit of FIG.2.

Referring lnow to FIG. l, an input signal source 2 is shown foraccepting and amplifying an input signal of predetermined waveform 4such as a positive-going sawtooth. Two substantially symmetrical outputamplifiers 6, 8 are coupled to the signal source 2 in such manner, to beeX- plained below, that when one is cut ofi the other conducts mostheavily and when the conducting one swings toward cutoff in response toa given input signal the nonconducting one swings toward saturation inresponse to the same signal, whence the output voltages, represented bywaveforms 10, 12, of the two output amplifiers 6, 8 are inverse to eachother. A feedback loop 14 from the first output amplifier 6 to the inputsignal source 2 provides overall inverse feedback for improvinglinearity.

FIG. 2 shows the input signal source 2 including an input couplingcapacitor 16 and resistor 18 and a preamplifier 20. The preamplifier 20includes two gain stages comprising first and second transistors 22, 24in cascade and a low impedance coupling circuit comprising a thirdtransistor 26 in an emitter-follower circuit configuration. Linearity isimproved by current feedback from the second transistor 24 to the firsttransistor 22 by way of a feedback resistor 28. A first Zener diode 30couples the output of the second transistor 24 directly to theemitter-follower transistor 26 while shifting the average level of theamplified signalV developed for application -to the output amplifiers 6,8.

The first output amplifier 6 comprises fourth, fifth, and sixthtransistors 32, 34, 36 with their collector-toemitter current pathsconnected in series to form a dynamic first conductor, and the secondoutput amplifier 8 comprises seventh, eighth, and ninth transistors 38,40, 42 similarly connected to form a dynamic second conductor. Thephrase dynamic conductor is used herein to mean a circuit elementcomprising variable impedance elements connected in series and capableof conduction, nonconduction or partial conduction. First and secondload impedance elements 44, 46 are connected between a first source ofdirect current operating potential 48 and the collectors of the sixthand ninth transistors 36, 42, respectively. Biasing means are provided,including a combination of two stabilized voltage sources comprisingsecond and third zener diodes 50, 52 connected in series and, in seriestherewith, a parallel subcombination of a bleeder resistor 54 and acapacitor 56 for passing transients. One end of this combination isconnected to the first source of direct current operating potential 48and the other to a source of fixed reference potential 58, in this caseground. First and second base biasing resistors 60, 62 are respectivelyconnected between the anode of the third Zener diode 52 and the baseelectrodes of the transistors corresponding thereto, namely, ythe fifthand eighth transistors 34, 40, and third and fourth base biasingresistors 64, 66 are respectively connected between the anode of thesecond Zener diode S and the base electrodes of the transistorscorresponding thereto, namely, the sixth and ninth'transistors 36, 42.

The effect of the transistor series arrangement of the first outputamplifier 6 is tov provide'means for the division among the first-output amplifier transistors 32, 34, 36 of the total potential dropbetween the collector of the sixth transistor 36 and the emitter of thefourth transistor 32, none of the transistors being separately capableof withstanding a collector-to-emitter voltage as high as the requiredtotal potential drop. Moreover, by matching the first output amplifiertransistors`32, 34,

36 with respect to current gain and by suitably proportioning the valuesof the first output amplifier base resistors 60, 64 the instantaneouscollector-to-emitter voltages appearing across the first outputamplifier transistors 32,34, 36 will be equaliZed over the signal cycle.Like results, that is, the division of Vtotal potential drop :and theequalizing of instantaneous collector-to-emitter voltages, are achievedin the operation of the second output amplifier 8 by matching the secondoutput amplifier transistors 38, 40, 42 with respect to current gain andproportioning the values of the second output amplifier base resistors62, 66. Y

T o obtain output voltage waveforms 10, 12 (FIG. 1) comprising signalswhich are inverse to each other the emitter-follower transistor 26 iscoupled to the first output amplifier 6 by directly connecting theemitter-folA lower transistor 26 and the base electrode of the fourthtransistor 32 and by connecting conductor-current-determining impedanceelement 68 between the emitter of the seventh transistor 38 and theemitter-follower transistor 26, another conductor-current-determiningimpedance element 70 being connected between vthe emitter of the fourthtransistor 32 and a second source of direct current operating potential72, `and the base electrode of the seventh transistor 38 being connectedto an adjustable nter-mediate tap of a potentiometer 74 included amongthe biasing means and connected between the source of fixed referencepotential 58 and the secondV source of direct current operatingpotential 72.

As a result of this arrangement the fourth transistorV 32 is biased tobe nonconducting and the seventh transistor V38 to be conducting duringthe quiescent portion of the input signal waveform 4 (FIG. 1). Also as aresult of this arrangement a positive-going signal from 4theemitter-follower transistor 26. will drive the .fourth transistor 32toward conduction and the seventh tranf sistor 38 toward nonconduetionsimultaneously, and a negative-going signal from the emitter-followertransistor 26 will have the opposite effects.

FIG. 2 shows a first protective diode 76 connected between the collectorelectrode of the fourth transistor 32 and the anode of the third Zenerdiode 52., Italso shows a second protective diode 78 connected'betweenthe collector electrode of the fifth transistor 34 and the anode ofthesecond Zener diode 50. The first protective diode 76 prevents thecollector of theV fourth transistor 32 from going more positive than theanode of the -third Zener diode 52 whenever the fourth transistor 32vis` in a nonconducting condition while the fifth and sixth transistors34, 36 are conducting. It is to be noted in' this connection that thestored charge in the junctions of the fifth and sixth transistors 34, 36may n-ot dissipate as fast as the charge stored in thefjunctions of thefourth transistor 32. This depends on the relative time constantsinvolved. Thus, if a negative-going volt- Y age step is impressed uponthe base of the fourth tran- Y sistor 32 by the emitter-followertransistor 26, the fourth transistor 32 will stop conducting quicklybecause minority carrier charges in the base-emitter junction of thefourth transistor 32 Iwill be quickly Withdrawn into the emitter circuitof the emitter-follower transistor 26, which is not only a low impedancecoupling circuit in general, but which is preferred here because itsoutput `impedance is lowered still further whenever it develops anegative-going signal. By way of contrast, however,

the fifth and sixth transistors 34, 36 have no such 10W impedance sinkfor their stored minority carriers, and they therefore remain inconduction for a longer time. In the absence of the first protectivediode 76 the collectortoemitter voltage of the fourth transistor 32would, during the decay period of the `fifth` transistor 34, approachthe total potential drop between the first source of direct currentoperating potential 48` and the emitter of the fourth transistor 32, adrop which may be far in excess of the rated breakdown voltage of thefourth transistor 32. It should be noted, additionally that the fifthtransistor 34 is protected by the second protective diode 78 in asimilar manner when the fifth transistor 34 stops collector-emitterconduction and loses of the second Zener diode 5t) through the thirdbase-.i biasing impedance element 64, the base-emitter junction of thesixth transistor 36, the collector-emitter path of the fifth transistor34 and the first protective diode 76 to the anode of the third Zenerdiode 52. If there is base-emitter current fiow in the sixth transistor36, Aits collector-emitter impedance is low, its collector-emittercurrent flows, and its collector-emitter voltage .drop is less thanbreakdown rating.

A third protectivediode 80 is connected between the collector of theseventh transistor 38 and thefanode of the third Zener diode 52, While afourth protective diode 82 is connected between the collector of theeighth transistor 40 and the anode of the second Zener diode 50. Theserespectively serve purposes with respect to the seventh and eighthtransistorsV 38, 40 entirely analogous to the purposes respectivelyserved by the first and sec. ond protective diodes 76, 78 with respectto the fourth` and fifth transistors 32, 34.

Other diodes 84, 86, 88, are connected directly between the emitter andbase electrodes of the fifth, sixth, eighth, and ninth transistors 34,36, 40, 42 respectively, to prevent reverse base-emitter bias frombuilding up as a result of stray capacitance.

The resistor 54 connected between the anode of the third Zener'diode 52and the source of fixed reference po tential 5S acts as a bleederresistor to maintain current in the second yand third Zener diodes 50,52. The capaci-` tor S6 connected in parallel withthe resistor 54supplies the necessary current to the protective diodes 7678, 80, 82during the transient which occurs whenever the fourth, fifth, seventh,or eighth transistors 32, 34, 38, 40 stop conducting. The second andthird Zener diodes 50,4 52"` cannot supply this transient currentbecause they are poled in the wrong direction to do so. The -capacitanceof the.` capacitor 56 is many orders of magnitude greater than With theinput voltage waveform 4 to the preamplifier 20 (FIG. 2) comprising asawtooth signal having a peak-tot peak value of 0.3 volt, the secondtransistor 24 provides` a first intermediate voltagewaveform 92comprising a sawtooth signal having a value of approximately voltspeak-to-peak. A second intermediate voltage waveform (not shown) appliedto the emitter-follower transistor comprises a signal of the samesawtooth configuration as the first intermediate voltage waveform 92,but its average level with respect to ground has been droppedapproximately 62 volts by the first Zener diode 30 (FIG. 2). A thirdintermediate voltage waveform 94 comprises the signal which is appliedby the emitter-follower transistor 26 (FIG. 2) to the base electrode ofthe fourth transistor 32 (FIG. 2) and the conductor-current-determiningimpedance element 68 connected to the emitter of the seventh transistor38.

Because of the vcoupling arrangements between the two output amplifiersy6, 8 and the preamplifier 20, explained heretofore, the collectors ofthe fourth, fifth, and sixth transistors 32, 34, 36 respectively exhibitfourth and fifth intermediate voltage waveforms 96, 98 and the firstoutput voltage waveform 10, while the collectors of the seventh, eighth,and ninth transistors 38, 40, 42 respectively exhibit sixth and seventhintermediate voltage waveforms 100, 102 and the second output voltagewaveform 12 which are inverse to the first three. It will be noticedfrom these waveforms that the transistors in each output amplifier 6, 8operate together to divide the full defiection voltage among themselves.For example, in the quiescent state before time to or at time t3 thefourth, fifth, and sixth transistors 32, 34, 36 in the first outputamplifier 6 are noncondu-cting andthe respective collector potentialswith respect to ground are 50, 0, and 250 volts, indicating equalcollector-to-emitter potentials of about 100 volts, whereas the seventh,eighth, and ninth transistors 38, 40, 42 in the second output amplifier8 are conducting and the respective collector potentials with respect toground are approximately -50 volts indicating negligiblecollector-to-emitter voltages.

At time to, when the positive-going portion of the savvtooth signal ofthe third intermediate voltage waveform 94 is applied to the base of thefourth transistor amplifier 32 it is also applied to theconductor-current-determining impedance element 68 connected to theemitter of the seventh transistor 38. As a result, during the periodbetween to and t2 as for example at time t1 the fourth, fifth and sixthtransistors 32, 34, 36 are driven toward full conduction, lowering theircollector voltages proportionately, as shown in the fourth and fifthintermediate voltage waveforms 96, 98 and the first output voltagewaveform 10 to a minimum ofV -50 volts. Also as a result, the seventh,eighth and ninth transistors 3S, 40, 42 are meanwhile driven towardcutoff, raising their collector voltages proportionately, as shown inthe sixth and seventh intermediate voltage waveforms 100, 102 and thesecond output voltage waveform 12 to respective maxima of 50, 150, and250 rvolts with respect to ground.

At time t2, when the input voltage waveform 4 drops sharply, the firstintermediate voltage waveform 92, t-he second intermediate waveform (notshown) and the third intermediate waveform 94 also drop sharply as aresult, and the fourth, fifth and sixth transistors 32, 34, 36 areaccordingly driven sharply to cutoff, raising their collector voltagesfrom -50 to 50, 150 and 250 respectively. At the same time the seventh,eighth and ninth transistors 38, 40, 42 are accordingly driven sharplyinto full conduction, reducing their collector voltages from respectivevalues of 50, 150, 250 to a common value of 50.

If the first and second output voltage waveforms 10, 12 are not comparedto a fixed reference potential such as ground but are instead comparedwit-h each other, the potential difference is as shown in the deflectionvoltage waveform 104. This shows that the voltage excursion of theoutput terminal of the first output amplifier 6 is from +250 volts to 50volts concurrently with an excursion of the output terminal of thesecond output amplifier from 6 -50 volts to +250 volts. The resultingtotal swing is 600 volts, being the algebraic sum Referring now to FIG.4, a portion of a cathode ray tube (CRT) 106 is shown in front and sideviews. Also shown are an electron gun 108, a pair of deflection plates110, 112 and an electron beam 114 terminating in a spot 116 on the CRTscreen. If the collector electrodes of the sixth and ninth transistors36, 42 are respectively connected to the deflection plates 110, 112 andif the input voltage waveform 4 is fed into the preamplifier 20, thedeflection voltage waveform 104will cause a deflection of the electronbeam 114 and a corresponding sweep of spot 116 as shown in FIIG. 4a fortime to, 4b for time t1 and 4c for an instant before time t2, assumingappropriate values for the energy of the electron beam and for the CRTdimensions.

The foregoing description has been exemplary only and not intended tolimit the scope of the invention to the device illustrated in thedrawings. FIG. 2, for example, shows -NJP-N transistors in the outputamplifiers 6, 8, yet P-N-P transistors would do equally well withappropriate adjustment of operating and biasing potentials. Similarly,any low impedance voltage source or voltage regulator would equally wellserve the purpose of the second and third zener diodes 50, 52, thoughperhaps at some sacrifice in the way of weight or volume.

yOther alternative embodiments of the present invention include asemiconductor amplifier as described above but without the second outputamplifier 8 and`another semiconductor amplifier with either twosemiconductors or more than three semiconductors connected in series in'the output amplifiers. If the second output amplifier 8 were eliminated,of course, the output would be limited to the output of the first outputamplifier with respect to ground or some other reference point. Theadvantage of changing the number of semiconductors in each amplifierwould be that both smaller and larger deflection voltage swings could beproduced.

Other embodiments include other arrangements for coupling the inputsignal source 2 to the output ampli- Ifiers 6, 8 such as the use of acommon emitter impedance element (not shown) for the fourth and seventhtransistors 32, 38 or, alternatively, the use of separate emitterimpedance elements for those transistors 32, 38 meanwhile coupling thebase electrodes thereof to input signal means providing oppositelyphased signals. In connection with the circuit means for coupling theoutput amplifiers 6, 8 to the input signal source 2, note that theemitter-follower circuit configuration utilized for the third transistor26 is only one of several possible low impedance coupling circuits andfurther, that a low impedance signal source, while required inconnection with the circuit means utilized for coupling the outputamplifiers 6, y8 to the input signal source 2 in the preferredembodiment, may not be required where other circuit means are used forsuch coupling.

There has thus been disclosed a semiconductor amplifier for providinglarge output fvoltages which has advantages in weight, volume, and powerconsumption over vacuum tube defiection amplifiers known heretofore andwhich has advantages in voltage output and reliability oversemiconductor amplifiers known heretofore.

What is claimed is:

1. A linear semiconductor amplifier for providing output voltages largerthan those which can be provided by a single semiconductor comprising:

a low impedance source of input signals of predetermined waveformincluding input means for providing said signals and a multistagepreamplifie for amplifying said signals coupled with said input means,said preamplifier including feedback means coupled between stagesthereof for improving linearity of the amplifier signals and including alow impedance coupling circuit for developing said amplifier signals;

first and second sources of direct current operating potential and asource of fixed reference potential;

sponding Semiconductor device for limiting theI instantaneouscollector-emitter voltage of said preceding semiconductordevice to lessthan breakdown potential.

first and second pluralities of' semiconductor devices 5;

including a collector-emitter current path and a control electrode forcontrolling current in said path,

the paths of the semiconductor devices of said first plurality beingconnected in series to provide a dynamic first conductor withonetelectrode of the path mined'waveform including input means forprovid ing said signals and a multistage preamplifier for of a first ofthe semiconductor devices of said first 10 amplifyingl said signalscoupled with said input plurality forming a -first terminal of saidfirst conmeans, said preamplifier including feedback means ductor andone electrode of the path of a second coupled between stages thereof forimproviding lineof the semiconductor devices of said first pluralityarity of the amplified signals and a low impedance forming a secondterminal of said'first conductor, 15 coupling circuit for developingsaid amplified signals; the paths of the semiconductor devices of saidsecfirst and second sources of direct current operating ondpluralitybeing connected in series to provide a potential and a source of fixedreference potential; dynamic second conductor with one electrode of thefirst and second numerically equal pluralities of semipath of a first ofthe semiconductor devices of said conductor devices including acollector-emitter cursecond plurality forming a first terminal of saidsecrent path and a control electrode for controlling ond conductor andone electrode. of the path of a current in said path, the paths of thesemiconductor second of the semiconductor devices of said second devicesof said first plurality being connected in plurality forming a secondterminal of said second series to provide a dynamic first conductorwithone conductor, first and second load impedance elements electrode ofthe path of a first of the semiconductor being respectively connectedbetween said first terrnidevices of said first plurality forming a firstterminal nals and said first' source of direct current operating of saidfirst conductor and one electrode of the path potential, and additionalfeedback means being couof a second of the semiconductor devices of saidpled between one of said first terminals and said pre- Ifirst pluralityforming Va second terminal of said first amplifier lfor improvinglinearity of said output voltconductor, the paths' of the semiconductordevicesy ages; `of said second plurality being connected in series`biasing means for each of said semiconductor devices to provide adynamic second conductor with one .ingiuding an adjustabiy tappedimpcdanceelement electrode of the path of a first of the semiconductorconnected between said source of fixed reference devices of Said Secondplurality forming a first terpotential and said second source of directcurrent minal of said second conductor and one electrode operatingpotential and including a stabilizedk voltage of the path 0f a Second ofthe semiconductor devices source for each of said semiconductor devicesother of said second plurality forming a second terminalv than saidsecond semiconductor devices and a bias of said second conductor, firstand second load imcurrent-determining impedance element connectedpedance elements being respectively connected bebetween each of saidstabilized voltage sources and tween Said irSt terminals and said firstsource of the control electrode of the corresponding semicondircctculrcntv operating Potential, and additional ductor device, said biasVcurrent-determining impedfeedback means being coupled between one of`said ance element connected to each of said corresponding firstterminals and Said preamplifier for improving semiconductor devices ofsaid first plurality being linearity 0f Said Output voltages;` fproportioned and the semiconductor devices 0f Said` biasing .means foreach of said semiconductor devices first plurality being matched withrespect to current including an adlustably tapped irnPcdancc clclncntgain to provide substantially equal instantaneous connected between saidsource of fixed reference voltage drops across each of said devicesof'said first Potential and Said Second SOUrce 0f direct currentplurality, and said bias current-determining impedoperating Potentialand including a Stabilized Voltage ance element Connected to each ofSaid Correspond- SOUI'Ce fOl' Cach pair Of Said Semiconductor (leVlCeSing Semiconductor devices of said Second piuraiity of like order in saidconductors other than said sec- :being proportioned and thesemiconductor devices ond Semiconductor devices and a bias currentofsaid second plurality being matched with respect determining impedanceelement connected between to current gain to provide substantially equalinstan- Y each of said stabilized voltage sources and the con-` taneousvoltage drops across each of said devices of trol electrodo of cach ofthc Corresponding semicon- Said Second piuraiity; ductor devices, saidbias current-determining impedcircuit means for determining current flowin said conanco clement Connected to each of said Corresponding ductorsand providing oppositely phased changes in Semiconductor dcViccs of said1Llrst plurality being current magnitude therein in response to saidinput Proportioncd and the Semiconductor devices of said f signalsincluding a conductorv current-determining 'first plurality boingrnatcllcd With rcsPcct t0 Current impedance element connected betweensaid second G9 gain to Provide Substantially equal instantaneousterminal of said second conductor and said source Voltage drops aCrOSScach Of Said devices of said first of input signals and includinganother conductor plurality, and Said bias current-determiningimpedcurrent-determining impedancey element connected anco clementconnected to cach of said correspond' between said second terminal ofsaid first conductor lng semiconductor devices of said Second pluralityand said second source of direct current operating 65 being proportionedand the semiconductor devices of potential, said control electrode ofsaid second semisaid second plurality being matched with respectconductor of said first plurality being connected to to current gain toprovide substantially equal instansaid low impedance coupling circuit,andV said control taneous voltage drops across each of saiddevices ofelectrode of said second semiconductor of said secsaid second plurality;t ond plurality being connected to an intermediate tap circuit means fordetermining current flow in said conof said adjustably tapped impedanceelement; and ductors and providing oppositely phased changes inunilaterally conducting protective means connected becurrent magnitudetherein in response to said input tween each of said stabilized voltagesources and the signals including a conductor current-determiningcollector electrode of the current path of the semiimpedance elementconnected between said second conductor device immediately precedingsaid correterminal of said second conductor and said source 9 10 ofinput signals and including another conductor of said precedingsemiconductor devices to less than current-determining impedance elementconnected breakdown potential. between said second terminal of saidfirst conductor and said second source of direct current operatingReferences Cited by the Examiner potential, said control electrode ofsaid second semi- 5 UNITED STATES PATENTS conductor of said rstplurality being connected to said low impedance coupling circuit, andsaid control IEDhrel "golgls electrode of said second semiconductor ofsaid sec- 3"()18446 1/196'2 Kud 313,0 18

ond plurality being connected to an intermediate tap 3024422 3/1962 J uson i330 18 of said adjustably tapped impedance element; and 10 anssonunilaterally conducting protective means connected be- FOREIGN PATENTStween each `of said stabilized voltage sources and the collectorelectrodes of the current paths of the re- 1143859 2/1963 Germany'spective semiconductor devices immediately .preced- ROY LAKE, primaryExaminer.

ing said corresponding semiconductor devices for 15 limiting theinstantaneous collector-emitter voltage F' D' PARIS Assstam Exammer-

1. A LINEAR SEMICONDUCTOR AMPLIFIER FOR PROVIDING OUTPUT VOLTAGE LARGERTHAN THOSE WHICH CAN BE PROVIDED BY A SINGLE SEMICONDUCTOR COMPRISING: ALOW IMPEDANCE SOURCE OF INPUT SIGNALS OF PREDETERMINED WAVEFORMINCLUDING INPUT MEANS FOR PROVIDING SAID SIGNALS AND A MULTISTAGEPREAMPLIFIER FOR AMPLIFYING SAID SIGNALS COUPLED WITH SAID INPUT MEANS,SAID PREAMPLIFIER INCLUDING FEEDBACK MEANS COUPLED BETWEEN STAGESTHEREOF FOR IMPROVING LINEARITY OF THE AMPLIFIER SIGNALS AND INCLUDING ALOW IMPEDANCE COUPLING CIRCUIT FOR DEVELOPING SAID AMPLIFIER SIGNALS;FIRST AND SECOND SOURCES OF DIRECT CURRENT OPERATING POTENTIAL AND ASOURCE OF FIXED REFERENCE POTENTIAL; FIRST AND SECOND PLURALITIES OFSEMICONDUCTOR DEVICES INCLUDING A COLLECTOR EMITTER CURRENT PATH AND ACONTROL ELECTRODE FOR CONTROLLING CURRENT IN SAID PATH, THE PATHS OF THESEMICONDUCTOR DEVICES OF SAID FIRST PLURALITY BEING CONNECTED IN SERIESTO PROVIDE A DYNAMIC FIRST CONDUCTOR WITH ONE ELECTRODE OF THE PATH OF AFIRST OF THE SEMICONDUCTOR DEVICES OF SAID FIRST PLURALITY FORMING AFIRST TERMINAL OF SAID FIRST CONDUCTOR AND ONE ELECTRODE OF THE PATH OFA SECOND OF THE SEMICONDUCTOR DEVICES OF SAID FIRST PLURALITY FORMING ASECOND TERMINAL OF SAID FIRST CONDUCTOR, THE PATHS OF THE SEMICONDUCTORDEVICES OF SAID SECOND PLURAITY BEING CONNECTED IN SERIES TO PROVIDE ADYNAMIC SECOND CONDUCTOR WITH ONE ELECTRODE OF THE PATH OF A FIRST OFTHE SEMICONDUCTOR DEVICES OF SAID SECOND PLURALITY FORMING A FIRSTTERMINAL OF SAID SECOND CONDUCTOR AND ONE ELECTRODE OF THE PATH OF ASECOND OF THE SEMICONDUCTOR DEVICES OF SAID SECOND PLUALITY FORMING ASECOND TERMINAL OF SAID SECOND CONDUCTOR, FIRST AND SECOND LOADIMPEDANCE ELEMENTS BEING RESPECTIVELY CONNECTED BETWEEN SAID FIRSTTERMINALS AND SAID FIRST SOURCE OF DIRECT CURRENT OPERATING POTENTIAL,AND ADDITIONAL FEEDBACK MEANS BEING COUPLED BETWEEN ONE OF SAID FIRSTTERMINALS AND SAID PREAMPLIFIER FOR IMPROVING LINEARITY OF SAID OUTPUTVOLTAGES; BIASING MEANS FOR EACH OF SAID SEMICONDUCTOR DEVICES INCLUDINGAN ADJUSTABLY TAPPED IMPEDANCE ELEMENT CONNECTED BETWEEN SAID SOURCE OFFIXED REFERENCE POTENTIAL AND SAID SECOND SOURCE OF DIRECT CURRENTOPERATING POTENTIAL AND INCLUDING A STABILIZED VOLTAGE SOURCE FOR EACHOF SAID SEMICONDUCTOR DEVICES OTHER THAN SAID SECOND SEMICONDUCTORDEVICES AND A BIAS CURRENT-DETERMINING IMPEDANCE ELEMENT CONNECTEDBETWEEN EACH OF SAID STABILIZED VOLTAGE SOURCES AND THE CONTROLELECTRODE OF THE CORRESPONDING SEMICONDUCTOR DEVICE, SAID BIASCURRENT-DETERMINING IMPEDANCE ELEMENT CONNECTED TO EACH OF SAIDCORRESPONDING SEMICONDUCTOR DEVICES OF SAID FIRST PLURALITY BEINGPROPORTIONED AND THE SEMICONDUCTOR DEVICES OF SAID FIRST PLURALITY BEINGMATCHED WITH RESPECT TO CURRENT GAIN TO PROVIDE SUBSTANTIALLY EQUALINSTANTANEOUS VOLTAGE DROPS ACROSS EACH OF SAID DEVICES OF SAID FIRSTPLURALITY, AND SAID BIAS CURRENT-DETERMINING IMPEDANCE ELEMENT CONNECTEDTO EACH OF SAID CORRESPONDING SEMICONDUCTOR DEVICES OF SAID SECONDPLURALITY BEING PROPORTIONED AND THE SEMICONDUCTOR DEVICES OF SAIDPLURALITY BEING MATCHED WITH RESPECT TO CURRENT GAIN TO PROVIDESUBSTANTIALLY EQUAL INSTANTANEOUS VOLTAGE DROPS ACROSS EACH OF SAIDDEVICE OF SAID SECOND PLURALITY; CIRCUIT MEANS FOR DETERMINING CURRENTFLOW IN SAID CONDUCTORS AND PROVIDING OPPOSITELY PHASE CHANGES INCURRENT MAGNITUDE THEREIN IN RESPONSE TO SAID INPUT SIGNALS INCLUDINGCONDUCTOR CURRENT-DETERMINING IMPEDANCE ELEMENT CONNECTED BETWEEN SAIDSECOND TERMINAL OF SAID SECOND CONDUCTOR AND SAID SOURCE OF INPUTSIGNALS AND INCLUDING ANOTHER CONDUCTOR CURRENT-DETERMINING IMPEDANCEELEMENT CONNECTED BETWEEN SAID SECOND TERMINAL OF SAID FIRST CONDUCTORAND SAID SECOND SOURCE OF DIRECT CURRENT OPERATING POTENTIAL, SAIDCONTROL ELECTRODE OF SAID SECOND SEMICONDUCTOR OF SAID FIRST PLURALITYBEING CONNECTED TO SAID LOW IMPEDANCE COUPLING CIRCUIT, AND SAID CONTROLELECTRODE OF SAID SECOND SEMICONDUCTOR OF SAID SECOND PLURALITY BEINGCONNECTED TO AN INTERMEDIATE TAP OF SAID ADJUSTABLY TAPPED IMPEDANCEELEMENT; AND UNILATERALLY CONDUCTING PROTECTIVE MEANS CONNECTED BETWEENEACH OF SAID STABILIZED VOLTAGE SOURCES AND THE COLLECTOR ELECTRODE OFTHE CURRENT PATH OF THE SEMICONDUCTOR DEVICE IMMEDIATELY PRECEDING SAIDCORRESPONDING SEMICONDUCTOR DEVICE FOR LIMITING THE INSTANTANEOUSCOLLECTOR-EMITTER VOLTAGE OF SAID PRECEDING SEMICONDUCTOR DEVICE TO LESSTHAN BREAKDOWN POTENTIAL.